The use of a "mouse" or a cursor position controller is well understood. Heretofore the mouse device has, for the most part, been a mechanical device such as that described in U.S. Pat. No. 3,541,521. Such mouse devices normally have a ball member which is rolled over a desk top, or table, or an enlarged pad. The surface over which the ball is moved must provide a sufficient coefficient of friction so that the ball does not skid. Inside the housing, of the prior art mouse, there are normally located two frictionally driven wheel arrangements which are oriented substantially perpendicular to one another. The wheels are frictionally coupled to the ball so that as the ball is moved on the surface of the desk, or the like, the movement of the wheels represents a resolution of the movement of the ball into components about two transverse axes. The movement of the wheels, in the prior art, has been quantified by employing potentiometers coupled to the wheels, or by employing perforated disks coupled to the wheels, with a light source and light sensitive device respectively disposed on either side of such a perforated disk. The last mentioned devices count perforations passing between the light source and the light sensitive device. Such prior art arrangements have suffered from skidding, or slipping, because of an improper surface, or a worn surface, over which the mouse is rolled; or from dirt being picked up by the roller and impeding the movement of the roller; or from having the dirt move into the path of the wheels which are frictionally coupled to the roller; or from the fact that the user failed to exert a sufficient downward pressure to provide the necessary frictional force; or from the dirt moving onto the electrical contacts, or the potentiometer, or across the face of the light emitter, or light receiver, to mention just some of the infirmities of the mechanical mouse.
Other cursor position controllers of the prior art have attempted to reduce the inherent problems of the mechanical mouse by employing an optical cursor control device. Such a system is described in U.S. Pat. No. 4,409,479. In the '479 system there is a light source within a housing and also enclosed therein are two X direction light sensitive devices and two Y direction light sensitive devices. The '479 system employs a planar grid which is made up of light absorbing bands and light reflecting spaces between the bands. The width of a band and the width of a space are identical. The light sensors detect the movement of the mouse in the X and Y directions and generate quadrature signals which are indicative of that movement. Such a system requires that the movement of the mouse be substantially commensurate with the bands and the spaces of the grid and that there be two sensors in each of the X and Y directions. The present system permits the user to move the sensor with less conformity to a grid and without employing two sensors in each of the X and Y directions.